Secondary control method and apparatus of parallel inverters in micro grid

Abstract

The present invention discloses a secondary control method and apparatus of parallel inverters in a micro grid, comprising: generating frequency and amplitude of fundamental voltage in the voltage instruction of inverter by droop control according to output voltage and output current of inverter to obtain a fundamental voltage instruction value; extracting voltage values and current values of a first and second AC signals from output voltage and output current of inverter, generating frequency instruction values of the first and second AC signals by droop control to obtain voltage instruction values of the first and second AC signals; regulating the output voltage of inverter according to the voltage instruction value of the first AC signal, the voltage instruction value of the second AC signal and the fundamental voltage instruction value.

What is claimed is: 
     
       1. A secondary control method of parallel inverters in micro grid, comprising:
 Step 1: generating a frequency instruction value and an amplitude instruction value of a fundamental voltage in the voltage instructions of the inverter by using a droop control according to an output voltage and an output current of the inverter, so as to obtain a fundamental voltage instruction value V fund ; 
 Step 2: extracting current values of a first AC signal and a second AC signal from the output current of the inverter, extracting voltage values of the first AC signal and the second AC signal from at least one voltage signal, generating a frequency instruction value of the first AC signal by using the droop control so as to obtain a voltage instruction value {circumflex over (v)} p * of the first AC signal, and generating a frequency instruction value of the second AC signal by using the droop control so as to obtain a voltage instruction value {circumflex over (v)} q * of the second AC signal; and 
 Step 3: regulating the output voltage of the inverter according to the voltage instruction value {circumflex over (v)} p * of the first AC signal, the voltage instruction value {circumflex over (v)} q * of the second AC signal, and the fundamental voltage instruction value V fund . 
 
     
     
       2. The secondary control method according to  claim 1 , wherein the at least one voltage signal is the output voltage of the inverter, or the at least one voltage signal is a voltage instruction value of the first AC small-signal and a voltage instruction value of the second AC small-signal at previous time. 
     
     
       3. The secondary control method according to  claim 2 , wherein before said Step 1, the method further comprises a Step 0: initializing the inverter, to set an initial value of a first dynamic parameter P 0 , an initial value of a second dynamic parameter Q 0 , an initial frequency ω 0  and an initial voltage E 0  respectively, wherein the first dynamic parameter P 0  is a droop bias for generating the frequency of the fundamental voltage, and the second dynamic parameter Q 0  is a droop bias for generating the amplitude of the fundamental voltage. 
     
     
       4. The secondary control method according to  claim 3 , wherein said Step 1 comprises:
 Step 11: calculating a current active power P and a current reactive power Q of the inverter according to a voltage instruction relevant to the output of the inverter and an output path current of the inverter; 
 Step 12: controlling the inverter to be a voltage source by using the droop control and obtaining the frequency instruction value ω* and the amplitude instruction value E* of the fundamental voltage by using the following formulae:
   ω*=ω 0   −m ·( P−P   0 ),
 
     E*=G   fE (( E   0   −E   f )− n ·( Q−Q   0 )),
 
 
 wherein m and n are the slopes of droop control lines and are both positive numbers, G iE  is a regulator, and, E r  is a voltage amplitude; and 
 Step 13: obtaining the fundamental voltage instruction value V fund  according to the frequency instruction value ω* and the amplitude instruction value E* of the fundamental voltage. 
 
     
     
       5. The secondary control method according to  claim 3 , wherein said Step 2 comprises:
 Step 21: obtaining an active power {circumflex over (P)} p  of the first AC signal and an active power {circumflex over (P)} q  of the second AC signal respectively, according to voltage values and current values of the first AC signal and the second AC signal; 
 Step 22: updating the values of the first dynamic parameter P 0  and the second dynamic parameter Q 0  according to the active power {circumflex over (P)} p  of the first AC signal, the active power {circumflex over (P)} q  of the second AC signal, a secondary control frequency ω* and a secondary control voltage amplitude E s ; 
 Step 23: determining the frequency instruction value ω p * of the first AC signal and the frequency instruction value {circumflex over (ω)} q * of the second AC signal that are intended to be injected; and 
 Step 24: generating the voltage instruction value {circumflex over (v)} p * of the first AC signal according to the frequency instruction value {circumflex over (ω)} p * of the first AC signal and a preset amplitude instruction value Ê of the first AC signal, and generating the voltage instruction value {circumflex over (v)} q * of the second AC signal according to the frequency instruction value {circumflex over (ω)} q * of the second AC signal and a preset amplitude instruction value Ê of the second AC signal. 
 
     
     
       6. The secondary control method according to  claim 5 , wherein said Step 22 are performed by using the following formulae:
     P   0   =G   sω (ω r −ω s )+ G   p   {circumflex over (P)}   p ,
 
     Q   0   =G   sE ( E   r   −E   s )+ G   q   {circumflex over (P)}   q , 
 wherein, ω r  and E r  are a rated frequency and a rated voltage amplitude respectively, when the output of the inverter reaches a stable status; G sω  and G sE  are regulators; G p  is a gain from the active power of the first AC signal to the first dynamic parameter P 0 ; and G q  is a gain from the active power of the second AC signal to the second dynamic parameter Q 0 . 
 
     
     
       7. The secondary control method according to  claim 5 , wherein said Step 23 is performed by using the following formulae:
   {circumflex over (ω)} p *={circumflex over (ω)} p0   −{circumflex over (m)}·P   0 ,
 
   {circumflex over (ω)} q *={circumflex over (ω)} q0   −{circumflex over (n)}·Q   0 ,
 
 wherein {circumflex over (m)} and {circumflex over (n)} are droop slopes of the first AC signal and the second AC signal respectively, and are both positive numbers, and {circumflex over (ω)} p0  and {circumflex over (ω)} q0  are preset frequency base values of the first AC signal and the second AC signal respectively. 
 
     
     
       8. The secondary control method according to  claim 5 , wherein if said Step 21 is performed for the first time, the active power {circumflex over (P)} p  of the first AC signal and the active power {circumflex over (P)} q  of the second AC signal are both zero. 
     
     
       9. The secondary control method according to  claim 6 , wherein the orders of magnitudes of G p {circumflex over (P)} p  and G q {circumflex over (P)} q  are set to be the same as the orders of magnitudes of the dynamic parameters P 0  and Q 0 . 
     
     
       10. The secondary control method according to  claim 1 , wherein the secondary control method is performed for all the inverters in micro grid. 
     
     
       11. A secondary control apparatus of parallel inverters in micro grid, comprising:
 a fundamental voltage instruction value generation module, for generating a frequency instruction value and an amplitude instruction value of the fundamental voltage in the voltage instructions of the inverter by using a droop control according to an output voltage and an output current of the inverter, so as to obtain a fundamental voltage instruction value V fund ; 
 an AC signal voltage instruction value generation module, for extracting current values of a first AC signal and a second AC signal from the output current of the inverter, extracting voltage values of the first AC signal and the second AC signal from at least one voltage signal, generating a frequency instruction value of the first AC signal by using the droop control so as to obtain a voltage instruction value of the first AC signal, and generating a frequency instruction value of the second AC signal by using the droop control so as to obtain a voltage instruction value of the second AC signal; and 
 a regulation module, for regulating the output voltage of the inverter according to the voltage instruction value of the first AC signal, the voltage instruction value of the second AC signal, and the fundamental voltage instruction value V fund . 
 
     
     
       12. The secondary control apparatus according to  claim 11 , wherein the at least one voltage signal is the output voltage of the inverter, or the at least one voltage signal is a voltage instruction value of the first AC small-signal and a voltage instruction value of the second AC small-signal at previous time. 
     
     
       13. The secondary control apparatus according to  claim 12 , further comprising an initialization module for initializing the inverter, to set an initial value of a first dynamic parameter P 0 , an initial value of a second dynamic parameter Q 0 , an initial frequency ω 0  and an initial voltage E 0  respectively, wherein the first dynamic parameter P 0  is a droop bias for generating the frequency of the fundamental voltage, and the second dynamic parameter Q 0  is a droop bias for generating the amplitude of the fundamental voltage. 
     
     
       14. The secondary control apparatus according to  claim 13 , wherein the fundamental voltage instruction value generation module comprises:
 a first power calculation module, for calculating a current active power P and a current reactive power Q of the inverter according to a voltage instruction relevant to the output of the inverter and an output path current of the inverter; 
 a droop control module, for controlling the inverter to be a voltage source by using the droop control and obtaining the frequency instruction value ω* and the amplitude instruction value E* of the fundamental voltage, wherein the frequency ω* and the amplitude E* of fundamental voltage are obtained by using the following formulae:
   ω*=ω 0   −m ·( P−P   0 ),
 
     E*=G   jE (( E   0   −E   f )− n ·( Q−Q   0 )),
 
 
 wherein m and n are the slopes of droop control lines and are both positive numbers; G fE  is a regulator; and E f  is a voltage amplitude; and 
 a first voltage instruction value generation module, for obtaining the fundamental voltage instruction value V fund  according to the frequency instruction value ω* and the amplitude instruction value E* of the fundamental voltage. 
 
     
     
       15. The secondary control apparatus according to  claim 13 , wherein the AC signal voltage instruction value generation module comprises:
 an AC signal extraction module, for obtaining voltage values and current values of the first AC signal and the second AC signal according to the at least one voltage signal and the output current of the inverters; 
 a second power calculation module, for obtaining the active power {circumflex over (P)} p  of the first AC signal and the active power {circumflex over (P)} q  of the second AC signal according to the voltage values and the current values of the first AC signal and the second AC signal respectively; 
 a secondary control module, for updating the values of the first dynamic parameter P 0  and the second dynamic parameter Q 0  according to the active power {circumflex over (P)} p  of the first AC signal, the active power a of the second AC signal, a secondary control frequency ω s , and a secondary control voltage amplitude E s , and determining a frequency instruction value {circumflex over (ω)} p * of the first AC signal and a frequency instruction value {circumflex over (ω)} q * of the second AC signal that are intended to be injected according to the updated first and second dynamic parameters P 0  and Q 0 ; and 
 a second voltage instruction value generation module, for generating the voltage instruction value of the first AC signal according to the frequency instruction value of the first AC signal and a preset amplitude instruction value Ê of the first AC signal, and generating the voltage instruction value of the second AC signal according to the frequency instruction value of the second AC signal and a preset amplitude instruction value Ê of the second AC signal. 
 
     
     
       16. The secondary control apparatus according to  claim 15 , wherein the secondary control module updates the values of the first dynamic parameter P 0  and the second dynamic parameter Q 0  by using the following formulae:
     P   0   =G   sω (ω r −ω s )+ G   p   {circumflex over (P)}   p ,
 
     Q   0   =G   sE ( E   r   −E   s )+ G   q   {circumflex over (P)}   q , 
 wherein ω r  and E r  are a rated frequency and a rated voltage amplitude respectively, when the output of the inverter reaches a stable status; G sω  and G sE  are regulators; G p  is a gain from the active power of the first AC signal to the first dynamic parameter P 0 ; and G q  is a gain from the active power of the second AC signal to the second dynamic parameter Q 0 . 
 
     
     
       17. The secondary control apparatus according to  claim 15 , wherein the secondary control module determines the frequency instruction value {circumflex over (ω)} p * of the first AC signal and the frequency instruction value {circumflex over (ω)} q * of the second AC signal that are intended to be injected by using the following formulae:
   {circumflex over (ω)} p *={circumflex over (ω)} p0   −{circumflex over (m)}·P   0 ,
 
   {circumflex over (ω)} q *={circumflex over (ω)} q0   −{circumflex over (n)}·Q   0 ,
 
 wherein {circumflex over (m)} and {circumflex over (n)} are droop slopes of the first AC signal and the second AC signal respectively, and are both positive numbers, and {circumflex over (ω)} p0  and {circumflex over (ω)} q0  are preset frequency base values of the first AC signal and the second AC signal respectively. 
 
     
     
       18. The secondary control apparatus according to  claim 15 , wherein if the second power calculation module operates for the first time, the active power {circumflex over (P)} p  of the first AC signal and the active power {circumflex over (P)} q  of the second AC signal are both set to be zero. 
     
     
       19. The secondary control apparatus according to  claim 16 , wherein the orders of magnitudes of G p {circumflex over (P)} p  and G q {circumflex over (P)} q  are set to be the same as the orders of magnitudes of the dynamic parameters P 0  and Q 0 . 
     
     
       20. The secondary control apparatus according to  claim 11 , wherein the regulation module comprises:
 a voltage closed-loop regulation module, for obtaining a voltage regulation instruction value v ref  according to the voltage instruction value of the first AC signal, the voltage instruction value of the second AC signal and the fundamental voltage instruction value V fund ; and 
 a pulse width modulation module, for regulating the output voltage of the inverter according to the voltage regulation instruction value v ref .